Axiall said on Friday that it had rejected Westlake’s $1.4 billion takeover offer, saying it undervalued the company - an argument that Brigade Capital agreed with.

However, the hedge fund, which said it has a stake of about 2 percent in Axiall, said on Monday it was disappointed that the company had not engaged “more fully in substantive discussions” with Westlake to negotiate a higher offer.

Brigade Capital said in a letter to Axiall’s board that it opposed the use of a “poison pill” with respect to Westlake’s offer of $20 per share.

Westlake, a Houston-based manufacturer and supplier of petrochemicals, polymers and building products, had argued that the combined company would be more diversified and have a stronger financial profile than Axiall on its own.

Axiall shares were down 2.6 percent at $17.46 in afternoon trading, while Westlake was down 2.2 percent at $44.47. (Reporting by Amrutha Gayathri in Bengaluru; Editing by Savio D‘Souza)